Silicone defoamer is a white, viscous emulsion. It has been used in various industrial fields since the 1960s, but its large-scale and comprehensive rapid development began in the 1980s. As a silicone defoaming agent, its application fields are also very wide, and it has attracted more and more attention from all walks of life. In chemical, papermaking, coating, food, textile, pharmaceutical and other industrial sectors, silicone defoamer is an indispensable additive in the production process. It can not only remove foam on the liquid surface of the process medium during the production process, thereby improving filtration, Separation, gasification, liquid drainage and other effects of washing, extraction, distillation, evaporation, dehydration, drying and other processes to ensure the capacity of various materials holding and processing containers

Principle of action

Whenever we stir the liquid or introduce gas, many bubbles will be generated within the surface area of the liquid. Some bubbles generated by the liquid will quickly break and disappear. Some liquids not only do not disappear, but also accumulate more and more, forming foam. Foam is a dispersion system formed by a large number of bubbles dispersed in a liquid. The dispersed phase is gas and the continuous phase is liquid. The volume fraction of the foaming liquid is very small, and the foam occupies a large volume. The gas is separated by a continuous liquid film, forming bubbles of varying sizes, which accumulate to form foam.

The foaming medium is like surfactant, which adsorbs a layer of oriented surfactant molecules on the surface of the bubble. When it reaches a certain concentration, the bubble wall forms a solid film. Surfactant is adsorbed on the gas-liquid interface, causing the surface tension of the liquid surface to decrease, thereby increasing the gas-liquid contact surface, making it difficult for bubbles to merge. The relative density of bubbles is much smaller than that of the liquid itself. When the rising bubbles penetrate the liquid surface, they adsorb a layer of surfactant molecules on the liquid surface. Therefore, the bubble film with adsorbed surfactant exposed in the air is different from the bubble film in the solution. It contains two layers of surfactant molecules to form a bimolecular film. The adsorbed surfactant protects the liquid film. effect. The defoaming agent is to destroy and inhibit the formation of this film. The defoaming agent enters the bimolecular oriented film of the foam and destroys the mechanical balance of the oriented film to achieve the foam breaking effect.

The defoaming agent must be a substance that is insoluble in the foaming medium and can be dispersed into the foaming medium in the form of liquid droplets, liquid droplets surrounding solid particles, or solid particles. The defoaming agent has a lower surface tension than the foaming medium and can spontaneously enter the liquid film to burst the bubbles.

The defoaming agent is easy to spread on the surface of the solution and automatically spreads on the surface of the foam. It will take away a layer of solution on the adjacent surface, making the liquid film locally thinner and reaching a critical thickness. The liquid film will rupture and the foam will be destroyed. The faster the defoaming agent spreads on the surface of the solution, the thinner the liquid film will become, the faster the foam will be destroyed, and the defoaming effect will be strengthened. Therefore, the reason for defoaming is on the one hand that it is easy to spread, and the adsorbed defoaming agent molecules replace the foaming agent molecules, forming a film with poor strength. At the same time, part of the solution adjacent to the surface layer is taken away during the spreading process, making the foam liquid film thinner, reducing the stability of the foam, and making it easier to destroy.

An excellent defoaming agent must have both defoaming and foam-suppressing effects, that is, it should not only destroy foam quickly, but also prevent foam formation for a long time. The reason for this may be related to whether the critical micelle concentration of the foaming agent (surfactant) in the solution is exceeded. In excess solution, the defoaming agent (generally an organic liquid) may be solubilized, causing it to lose its ability to spread on the surface, and the defoaming effect is greatly reduced. After a period of time, as the defoaming agent is gradually solubilized, the defoaming effect weakens accordingly.

Components and functions

Defoaming agents are generally composed of a variety of components with different functions, namely main anti-foaming agents, auxiliary anti-foaming agents, carriers, emulsifiers or developing agents, stabilizers or compounding agents.

(1) Main anti-foaming agent: The main active component is usually an insoluble granular substance, such as hydrophobic silica, fatty amine, paraffin, etc. treated with silicone oil.

(2) Auxiliary defoaming agent: It is an active component that plays a regulating role, improves the surface effect of the main defoaming agent, and plays a synergistic effect on the main defoaming agent. Such as fatty alcohols, fatty acid esters, etc.

(3) Carrier: plays a supporting role in the main and auxiliary defoaming agents. Water is the most convenient and economical carrier.

(4) Emulsifiers and developing agents: These allow the active components of the defoaming agent to be immediately dispersed in the foaming medium and contact the surface more quickly, thus improving the development efficiency of the defoaming agent. Commonly used emulsifiers include organic esters and ethyl oxidation products.

(5) Stabilizers and compounding agents: They are additives that improve the stability and storage time of defoaming agents. The stabilizer of water-based defoaming agents is often a preservative to prevent the product from being destroyed by bacteria during storage. Commonly used compounding agents include oleic acid, hexylene glycol, etc.

3. Active components and properties of silicone defoamer:

(1) Active component: The main component of silicone defoamer is linear polysiloxane (English name: Polysiloxane, Silicones) (also known as silicone oil) that can remain liquid at room temperature as an active agent. Oxanes mainly include the following types;

Polydimethylsiloxane: The molecular formula is as follows:

Me 3 SiO(Me 2 SiO ) nSiMe 3

Silicone oil is a non-volatile oily liquid at room temperature. It is insoluble or has very little solubility in water, animal and vegetable oils and mineral oils. It can withstand both high and low temperatures. It is chemically inert, physically stable and has no biological activity.

(2) Performance of silicone defoamer: Silicone defoamer has three functions: foam breaking, defoaming and foam suppression.

(3) Characteristics of silicone defoamer

[Appearance] White viscous lotion

【PH value】6-8

[Water dilubility] 0.5%-5.0% foaming liquid dilution

【Volatile】Non-volatile matter

[Stability] 3000 rpm/20 minutes without delamination

[Ionic Characteristics] Non-ionic

[Temperature resistance characteristics] No demulsification, no oil drift, and no delamination at 130°C

Advantage

(1) Wide range of applications: Due to the special chemical structure of silicone oil, it is neither compatible with water or substances containing polar groups, nor with hydrocarbons or organic substances containing hydrocarbon groups. Due to the insolubility of silicone oil to various substances, it has a wide range of applications. It can be used for defoaming in water systems and in oil systems.

(2) Small surface tension: The surface capacity of silicone oil is generally 20-21 dynes/cm, which is smaller than the surface tension of water (72 dynes/cm) and general foaming liquids, and has better defoaming efficiency.

(3) Good thermal stability: Taking commonly used dimethyl silicone oil as an example, it can withstand 150°C for a long time and more than 300°C for a short time, and its Si-O bond does not decompose. This ensures that the silicone defoamer can be used within a wide temperature range.

(4) Good chemical stability: Since the Si-O bond is relatively stable, the chemical stability of silicone oil is very high and it is difficult to chemically react with other substances. Therefore, as long as the preparation is reasonable, silicone defoaming agents are allowed to be used in systems containing acids, alkalis, and salts.

(5) Physiologically inert: Silicone oil has been proven to be non-toxic to humans and animals, and its half-lethal dose is greater than 34 g/kg. Therefore, silicone defoamer (when combined with appropriate non-toxic emulsifiers, etc.) can be safely used in industries such as food, medical, pharmaceutical and cosmetics.

(6) Strong defoaming power: Silicone defoaming agents can not only effectively break the foam that has been generated, but also significantly inhibit foam and prevent the formation of foam. Its use is very small, as long as one millionth (1ppm) of the weight of the foaming medium is added, it can produce a defoaming effect. Its common range is 1 to 100ppm. Not only is the cost low, but it also does not pollute the defoamed material.

Ether modified silicone defoamer

Polyether modified silicone is a polyether-siloxane copolymer (referred to as silicon ether copolymer) made by introducing polyether segments into siloxane molecules. Polyether modified silicone defoamer is a new type of high-efficiency defoamer that organically combines the advantages of both. It selects polyether with strong anti-foaming ability and dimethyl silicone oil with strong hydrophobicity and rapid foam breaking as the main ingredients, and matches emulsifiers, stabilizers and other ingredients that can organically combine silicone oil and polyether. Foaming agent. It has the characteristics of low surface tension, rapid defoaming, long foam suppression time, low cost, low dosage, and wide application range. Polyether modification of silicone makes it have the advantages of Class II defoaming agent and becomes a defoaming agent with excellent performance and wide application prospects.

In the molecule of silicon ether copolymer, the siloxane segment is a lipophilic group and the polyether segment is a hydrophilic group. The polyethylene oxide chain energy in the polyether segment provides hydrophilicity and foaming properties, while the polyethylene oxide chain energy provides hydrophobicity and permeability, which has a strong effect on reducing surface tension. The groups at the end of the polyether chain also have a great influence on the properties of silicon ether copolymers. Common end groups include hydroxyl, alkoxy, etc. Adjusting the relative molecular weight of the siloxane segment in the copolymer can make the copolymer highlight or weaken the properties of silicone. Similarly, changing the relative molecular weight of the polyether segment will increase or decrease the proportion of silicone in the molecule, which will also affect the performance of the copolymer. Polyether modified silicone defoamer is easily emulsified in water and is also called "self-emulsifying defoamer". Above its cloud point temperature, it loses solubility in water and mechanical stability, and is resistant to acids, alkalis and inorganic salts, and can be used for defoaming under harsh conditions.

In order to improve the lipophilicity used in water-based inks, coatings, cutting fluids, etc., part of the methyl groups in the copolymer molecules of polyether-modified silicone are replaced with long-chain alkyl groups, which can achieve a more effective defoaming effect. In order to achieve better defoaming performance below the cloud point temperature, commercial self-emulsifying defoaming agents are usually equipped with dimethyl silicone oil - silica paste. At this time, at the cloud point temperature Polyether modified silicone surfactant can also be used as an emulsifier for dimethyl silicone oil to play a dispersing and emulsifying role.

Useful

Silicone defoaming agents have a wide range of uses and applications, including erythromycin, chloramphenicol, abamectin, gentamicin , penicillin, oxytetracycline, tetracycline, tylosin, glutamic acid, lysine, It is used as defoaming agent in the fermentation industry such as acid, citric acid and xanthan gum. It is also used in textile, printing and dyeing, coatings, dyes, papermaking, ink, oil fields, sewage treatment and other fields. When used in printing and dyeing, it has good compatibility with the additives in the dye bath and does not affect the color light and dye fastness.

There are many reports on the use of silicone as a spray defoamer. In the old dyeing process, dimethyl polysiloxane defoamers were generally used to achieve satisfactory defoamer effects and ensure uniform dyeing. However, the new dyeing process uses high-temperature and high-pressure machinery, in which the dyed material is moved by the spray of dyeing liquid and dyed at the same time. Although the foam produced can be defoamed by ordinary silicone defoamers, under high temperature and high pressure, ordinary silicone defoamers will produce film-like precipitation and cause spots on the dyed material. The use of block copolymers can overcome the above shortcomings, because these defoamer components can be soluble in cold water but not in hot water, so they can play a defoaming role. However, the defoaming effect of using only this copolymer defoamer is not satisfactory. If a certain amount of mist SiO 2 is added to the copolymer , a satisfactory defoaming effect can be achieved and a fabric with uniform dyeing can be produced. It is used for defoaming in high-temperature dyeing and fermentation processes of polyester fabrics. In addition, it can also be used for defoaming of diethanolamine desulfurization system and various oils, cutting fluids, antifreeze, water-based inks and other systems. It is also suitable for defoaming of uncured resin after photosensitive resin plate making in the printing industry. It is a very representative, excellent-performance and widely-used silicone defoaming agent.

Packaging, storage and transportation

Packed in 25kg plastic drum or 200kg plastic-coated iron drum; store in a cool place, transported as non-toxic and non-dangerous goods, pay attention to anti-freeze.